U.S. patent application number 10/575734 was filed with the patent office on 2007-06-21 for capacitor comprising a ceramic separating layer.
This patent application is currently assigned to Degussa AG. Invention is credited to Sven Augustin, Volker Hennige, Gerhard Hoerpel, Christian Hying.
Application Number | 20070139860 10/575734 |
Document ID | / |
Family ID | 34428365 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070139860 |
Kind Code |
A1 |
Hoerpel; Gerhard ; et
al. |
June 21, 2007 |
Capacitor comprising a ceramic separating layer
Abstract
An electrochemical capacitor including a separating layer on a
support. The separating layer represents a porous inorganic,
electrically non-conducting coating which is provided with
particles of compounds of the elements Al, Si, and/or Zr, the
particles being bonded to each other and to the support by an
inorganic adhesive. The support can represent a porous electrode or
a porous and planar substrate that is provided with polymer
fibers.
Inventors: |
Hoerpel; Gerhard; (Nottuln,
DE) ; Hennige; Volker; (Dulmen, DE) ; Hying;
Christian; (Rhede, DE) ; Augustin; Sven;
(Dorsten, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Degussa AG
Bennigsenplatz 1
Duesseldorf
DE
D-40474
|
Family ID: |
34428365 |
Appl. No.: |
10/575734 |
Filed: |
August 19, 2004 |
PCT Filed: |
August 19, 2004 |
PCT NO: |
PCT/EP04/51845 |
371 Date: |
April 13, 2006 |
Current U.S.
Class: |
361/311 |
Current CPC
Class: |
H01M 50/403 20210101;
H01M 50/44 20210101; H01G 11/04 20130101; H01G 9/155 20130101; Y02T
10/70 20130101; H01M 50/411 20210101; Y02E 60/13 20130101; H01G
9/02 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
361/311 |
International
Class: |
H01G 4/06 20060101
H01G004/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2003 |
DE |
103 47 568.0 |
Claims
1-21. (canceled)
22. A capacitor comprising: a separating layer, wherein the
separating layer is present on a carrier and is adhered thereto and
is a porous inorganic nonelectroconductive coating which comprises
particles of compounds of the elements Al, Si and/or Zr that are
adhered to each other and to the carrier by an inorganic
adhesive.
23. A capacitor according to claim 22, wherein the carrier
comprises woven or non-woven polymeric or glass fibers.
24. A capacitor according to claim 23, wherein the carrier is
flexible and less than 50 .mu.m in thickness.
25. A capacitor according to claim 23, wherein the polymeric fibers
are selected from fibers of polyacrylonitrile, polyamide, polyester
and/or polyolefin.
26. A capacitor according to claim 22, wherein the carrier is an
electrode configured for use as an electrode in a capacitor.
27. A capacitor according to claim 26, wherein the carrier is a
porous electrode configured for use as an electrode in a
capacitor.
28. A capacitor according to claim 26, wherein the separating layer
comprises metal oxide particles having an average particle size
greater than the average pore size of the pores of the electrode
that are adhered together by metal oxide particles which have a
particle size which is smaller than the pores of the porous
electrode.
29. A capacitor according to claim 26, wherein the separating layer
has a thickness of less than 100 D.sub.g and not less than 1.5
D.sub.g.
30. A capacitor according to claim 29, wherein the separating layer
has a thickness of less than 20 D.sub.g and not less than 5
D.sub.g.
31. A capacitor according to claim 28, wherein the metal oxide
particles having an average particle size greater than the average
pore size of the pores of the porous positive electrode are
Al.sub.2O.sub.3 and/or ZrO.sub.2 particles.
32. A capacitor according to claim 28, wherein the metal oxide
particles having an average particle size less than the average
pore size of the pores of the porous positive electrode are
SiO.sub.2 and/or ZrO.sub.2 particles.
33. A capacitor according to claim 28, wherein the metal oxide
particles having an average particle size greater than the average
pore size of the pores of the porous electrode have an average
particle size of less than 10 .mu.m.
34. A capacitor according to claim 22, wherein the separating layer
has a porosity in a range from 30% to 70%.
35. A capacitor according to claim 22, wherein the inorganic
adhesives are selected from oxides of the elements Al, Si and/or
Zr.
36. A capacitor according to claim 22, wherein the inorganic
adhesive comprises particles having an average particle size of
less than 20 nm and was produced via a particulate sol or comprises
an inorganic network of the oxides which was produced via a
polymeric sol.
37. A capacitor according to claim 22, further comprising an
inorganic network comprising silicon, the silicon of the network
being bonded via oxygen atoms to the oxides of the inorganic
coating and via an organic radical to the carrier which comprises
polymeric fibers.
38. A capacitor according to claim 22, wherein the adhered
particles of the compounds of the elements Al, Si and/or Zr that
are present in the separator have an average particle size in a
range from 0.5 to 10 .mu.m.
39. A capacitor according to claim 22, wherein the capacitor
comprises a nonaqueous electrolyte selected from propylene
carbonate, N,N-dimethylformamide, .gamma.-butyrolactone or
acetonitrile as solvent and also tetraalkylphosphonium or
tetraalkylammonium salts as conducting salts.
40. A capacitor according to claim 22, wherein the separating layer
is obtainable by applying a suspension to the carrier and
solidifying the suspension on and in the carrier by at least single
heating, the suspension comprising a sol as inorganic adhesive and
at least one fraction of oxidic particles selected from the oxides
of the elements Al, Zr and/or Si.
41. A capacitor according to claim 40, wherein the suspension is
heated on the carrier at a temperature in the range from 170 to
280.degree. C. for from 0.5 to 10 minutes.
42. The use of a capacitor according to claim 22 as a store for
electrical energy in vehicles.
Description
[0001] The present invention relates to a capacitor which comprises
a ceramic separating layer.
[0002] Conventional capacitors store electrical energy on two
mutually opposite capacitor plates which are separated by a
dielectric. There are different types:
1. Wound capacitors: the metal plates in wound capacitors are
firmly wound up with a tape dielectric to form a wound coil. The
wound coil is usually accommodated in a metallic can and sealed off
with a potting compound to guard against moisture.
2. Paper capacitors: here the dielectric is formed by two or more
plies of cellulose paper. The metallic plates are formed by
aluminum foils. The connection wires have been welded onto thin
metal sheets, which are included in the wound coil.
[0003] 3. Film capacitors: their dielectric is composed of plastics
films such as polypropylene, polyester or polycarbonate. In the
case of film/foil capacitors, the metal plates are aluminum foils.
In the case of metalized film capacitors, the metal plates are
coatings formed by vapor depositions on the plastic films.
4. Electrolytic capacitors: their dielectric is a thin oxidic
layer. This makes it possible to fabricate small capacitors having
large capacities.
5. Ceramic capacitors: their dielectric is a ceramic material.
Small-scale ceramic capacitors are constructed as tubular and disk
capacitors.
[0004] Electrochemical capacitors (ECs), also known as
supercapacitors or ultracapacitors, store energy in the electric
field of the electrochemical double layer. Applications involving
an extremely large capacity are met using porous electrodes having
a very large surface area. State of the art ECs cover the range
between conventional capacitors (high power density, low energy
density) and batteries or fuel cells (low power densities, high
energy densities). The state of the art is surveyed in R. Kotz et
al (Electrochimica Acta 45 (2000), 2483ff) and M. Mastragostino et
al (Advances in Lithium-Ion Batteries, Kluwer Academic New York
(2002), pages 481 to 505). Various types of electrochemical
capacitors are distinguished in principle: [0005] 1. Double-layer
capacitors: "classic" variant, where the electric energy is stored
in an electric double layer on the electrode surface. A typical
electrode material here is graphite (natural, artificial,
nanotubes, . . . ) having very, large surface areas of up to 2500
m.sup.2/g. [0006] 2. Polymeric capacitors: pseudo-capacitor
behavior by virtue of p- and n-doping in polymers having conjugated
.pi.-electron systems. [0007] 3. Metal oxide capacitors: likewise
pseudo-capacitor behavior by virtue of fast, reversible Faradic
protonation of electrode surface. The typical electrode material
here is RuO.sub.2 in an acidic electrolyte.
[0008] A porous separator keeps the electrodes mechanically
separated in electrochemical capacitors. The electrolyte comprises
aqueous or nonaqueous solvents together with a suitable conducting
salt. Polymeric membranes are used as separators in aqueous
systems, while paper or a polyolefin, such as for example
polyethylene (PE) or polypropylene (PP), are used as separators in
nonaqueous systems. These separators exhibit low thermal stability,
which is why simple welding is not possible for cell assembly and,
secondly, the separator will melt or decompose when the capacitor
gets too hot in operation, which results in destruction of the
capacitor.
[0009] It is an object of the present invention to provide a
capacitor which has superior thermal stability and is simple to
produce.
[0010] It has now been found that, surprisingly, the use of ceramic
separating layers on carriers as separators improves the thermal
stability of capacitors and such separating layers are simple to
produce. The separating layers can be applied both to electrodes as
carriers (separator electrode unit) or else to carriers comprising
polymeric fibers. These various ways of producing the separating
layer make it possible for the capacitor of the present invention
to be produced by adding few if any modifications to the usual
hitherto customary manufacturing operations for capacitors.
[0011] Traditionally, a separator for electrochemical capacitors is
a thin porous electroinsulating material possessing high ion
perviousness, good mechanical strength and long-term stability to
the chemicals and solvents used in the system, for example in the
electrolyte of the electrochemical cell. The separator in an
electrochemical cell shall provide complete electronic insulation
of the cathode from the anode.
[0012] Separators used at present consist predominantly of porous
organic polymeric films or other organic or inorganic nonwoven
materials, such as papers for example. These are produced by
various companies. Important producers here are: Celgard, Tonen,
Ube, Asahi, Binzer, Mitsubishi, Daramic and others.
[0013] Most separators lack mechanical stability and tend to lead
to short circuiting, with the result that it is impossible to
achieve a long use life. A substantial disadvantage of organic
polyolefinic separators is their low thermal stability limit of
below 150.degree. C. Even brief attainment or exceedance of the
melting point of these polymers leads to substantial melting of the
separator and to destruction of the capacitor. The use of such
separators is therefore in general not safe, since these separators
and hence the capacitors are destroyed on attainment of higher
temperatures, especially of above 150.degree. C. or even
180.degree. C. Moreover, polyolefinic separators are extremely
apolar. But since the electrolytes used are mostly very polar,
substantial wetting problems occur. This leads to extremely long
fill times of the capacitors with the electrolyte and also to a
very limited choice of usable electrolytes.
[0014] Separators comprising ceramic coatings on various substrates
have recently been developed in the field of battery separators.
For instance, DE 198 38 800 C1 proposes an electrical separator
having a compositic structure that comprises a sheetlike, flexible
substrate which has a multiplicity of openings and supports a
coating. The material for the substrate is selected from metals and
the coating is an uninterrupted porous nonelectroconductive ceramic
coating. The use of a ceramic coating promises thermal and chemical
stability. The separators, which as exemplified comprise a carrier
or substrate composed of electrically conducting material, however,
have been determined to be unsuitable for electrochemical cells,
since the coating has proved impossible to produce over a large
area without defects at the thickness described. Short circuiting
accordingly occurs very readily. Moreover, such thin woven metal
fabrics as required for very thin separators are not commercially
available.
[0015] DE 101 42 622 showed that a material which comprises a
sheetlike, flexible substrate which has a multiplicity of openings
and supports a coating present on and in this substrate, the
material of the substrate having been selected from woven or
non-woven nonelectroconductive fibers of glass or ceramic or a
combination of such materials and the coating being a porous
electroinsulating ceramic coating and the resulting battery
separator being less than 100 .mu.m in thickness and bendable, can
be used to produce a battery separator which in conjunction with
the electrolyte has a sufficiently low resistance and yet has a
sufficiently large long-term stability. DE 102 08 277 reduced the
weight and the thickness of the battery separator for lithium high
energy batteries by utilizing a polymeric nonwoven.
[0016] That the separators described there are also useful in
capacitors, especially in capacitors without aqueous electrolytes,
however, has hitherto been neither recognized nor described. The
present invention therefore resides in the use of separators in
capacitors which comprise a separating layer on a porous carrier,
wherein the separating layer is a porous inorganic
nonelectroconductive coating which comprises particles of the
elements Al, Si and/or Zr that are adhered to each other and to the
carrier by an inorganic adhesive.
[0017] The present invention accordingly provides a capacitor which
comprises a separating layer, characterized in that the separating
layer is present on a carrier, preferably a porous carrier, and is
a porous inorganic nonelectroconductive coating which comprises
particles of compounds of the elements Al, Si and/or Zr that are
adhered to each other and to the carrier by an inorganic adhesive,
and also for its use as a store for electrical energy, for example
for use in vehicles.
[0018] The separators according to the present invention have the
advantage of being very readily wettable by organic polar solvents
in particular and, especially, of possessing good thermal
stability. Owing to thermal stability, not only is capacitor
assembly simpler (welding), but also the separator will not melt or
decompose in the event that a cell gets too hot in operation.
Especially a stack of capacitors that is needed to achieve higher
voltages becomes distinctly more outage-resistant as a result.
[0019] Owing to the better wettability of separators according to
the present invention, the electrochemical cell can be filled with
electrolyte very rapidly. This shortens capacitor manufacturing
time appreciably. Moreover, it is now also possible to use many
other solvents which are difficult or impossible to use together
with polyolefinic separators.
[0020] The construction of capacitors and also the production
thereof is discernible for example from EP 1202 299, U.S. Pat. No.
6,585,152, EP 1 314 174 and EP 1 212 763. More particularly,
capacitor construction and functioning is discernible from the
contribution of D. K. Haskell, A. C. Kolb and W. G. McMillan in
Encyclopedia of Applied Physics, Volume 6, pages 155 to 176, VCH
Publishers New York, 1993 and the references cited therein.
[0021] The capacitor according to the present invention and a
process for producing the separating layer present therein will now
be described without wishing to restrict the invention to these
embodiments.
[0022] The capacitor according to the present invention, which
comprises a (ceramic) separating layer, is characterized in that
the separating layer is present on a carrier, preferably a porous
carrier, and is adhered thereto and is a porous inorganic
nonelectroconductive coating which comprises particles of compounds
of the elements Al, Si and/or Zr, especially oxidic particles of
these elements, that are adhered to each other an to the carrier by
an inorganic adhesive.
[0023] The inorganic adhesive in the separating layer in the
capacitor according to the present invention is preferably selected
from oxides of the elements Al, Si and/or Zr. The inorganic
adhesive may for example comprise particles having an average
particle size of less than 20 nm and have been produced via a
particulate sol or an inorganic network of the oxides which was
produced via a polymeric sol.
[0024] It can be advantageous for the separating layer to further
comprise an inorganic network comprising silicon, the silicon of
the network being bonded via oxygen atoms to the oxides of the
inorganic coating and via an organic radical to the carrier which
comprises polymeric fibers. Such a network is obtained when an
adhesion promoter is used in the production of the separating layer
and this adhesion promoter is subjected to the thermal treatment
customary for the production process.
[0025] Depending on the type of capacitor, the separating layer can
comprise oxidic particles of the elements Al, Si and/or Zr in
different sizes. Preferably, capacitors according to the present
invention comprise a separating layer which comprise particles
having an average particle size in the range from 0.5 to 10 .mu.m
and preferably from 1 to 5 .mu.m. But larger and smaller particle
sizes are also conceivable, depending on the carrier used. It is
particularly preferable for the particles to be adhered using an
oxide of the metals Zr or Si. The separating layer ceramic material
formed via the particles and the inorganic adhesive, in the
capacitor according to the present invention, preferably has an
average pore size in the range from 50 nm to 5 .mu.m and more
preferably in the range from 80 nm to 800 nm.
[0026] The separating layer present in the capacitor according to
the present invention may be present on a very wide variety of
carriers. In a preferred embodiment, the separating layer is
present on a carrier which comprises fibers of polymers, glass
and/or ceramic, polymeric fibers being preferred. With this
embodiment of the capacitor according to the present invention, the
separating layer can be present on or on and in the carrier
mentioned and combine with the carrier to form a separator in the
usual sense.
[0027] Preferably, in this embodiment of the invention, the
capacitors according to the present invention comprise carriers
which are flexible and preferably less than 50 .mu.m in thickness.
Carrier flexibility ensures separator flexibility as well. Such
flexible separators are indispensable for example in wound
capacitors according to the present invention.
[0028] Preferably, the capacitor according to the present invention
comprises a separator having a carrier which is less than 30 .mu.m
and more preferably less than 20 .mu.m in thickness. To be able to
achieve sufficiently high performance capability, it has been
determined to be advantageous for most applications for the
separator according to the present invention to comprise a carrier
whose porosity is preferably above 50%, more preferably in the
range from 50% to 97%, even more preferably in the range from 60%
to 90% and most preferably in the range from 70% to 90%. Porosity
in this context is defined as the volume of the carrier (100%)
minus the volume of the fibers of the carrier, i.e., the fraction
of the volume of the carrier that is not taken up by material. The
volume of the carrier can be calculated from the dimensions of the
carrier. The volume of the fibers is calculated from the measured
weight of the nonwoven in question and the density of the fibers
and especially of the polymeric fibers. In a further embodiment of
the invention, the carrier is a nonwoven having a pore size in the
range from 5 to 500 .mu.m and preferably in the range from 10 to
200 .mu.m. It can be similarly advantageous for the carrier to have
a pore radius distribution where at least 50% of the pores have a
pore radius in the range from 75 to 150 .mu.m.
[0029] The porous (perforate) carrier preferably comprises woven or
non-woven polymeric or glass fibers. It is particularly preferable
for the carrier to comprise a glass or polymeric woven or nonwoven
or to be such a woven or nonwoven. The polymeric fibers in the
carrier are preferably nonelectroconductive fibers of polymers
which are preferably selected from polyacrylonitrile (PAN),
polyesters, for example polyethylene terephthalate (PET), polyamide
(PA) and/or polyolefin (PO), for example polypropylene (PP) or
polyethylene (PE) or mixtures of such polyolefins. When the
perforate carrier comprises polymeric fibers, however, polymeric
fibers other than those mentioned above can be used as well, as
long as they have the requisite thermal stability for the
production of the separators and capacitors and also are stable
under the operating conditions. In a preferred embodiment, the
carrier according to the present invention comprises polymeric
fibers having a softening temperature of above 100.degree. C. and a
melting temperature of above 110.degree. C. The carrier may
comprise fibers and/or filaments from 0.1 to 150 .mu.m and
preferably from 1 to 20 .mu.m in diameter and/or threads from 3 to
150 .mu.m and preferably from 10 to 70 .mu.m in diameter. When the
carrier comprises polymeric fibers, these are preferably from 0.1
to 10 .mu.m and more preferably from 1 to 5 .mu.m in diameter.
Particularly preferred flexible nonwovens, especially polymeric
nonwovens, have a basis weight of less than 20 g/m.sup.2 and
preferably in the range from 5 to 15 g/m.sup.2. This ensures a
particularly low thickness and high flexibility for the
carrier.
[0030] It is particularly preferable for the capacitor according to
the present invention to comprise a carrier which is a polymeric
nonwoven which is less than 30 .mu.m and preferably from 10 to 20
.mu.m in thickness. A very homogeneous pore radius distribution in
the nonwoven is particularly important for use in a separator
according to the present invention. A very homogeneous pore radius
distribution in the nonwoven leads in conjunction with optimally
adapted oxidic particles of a certain size to an optimized porosity
for the separator according to the present invention.
[0031] Depending on the intended use for the capacitor according to
the present invention and especially depending on to the
electrolyte/conducting salt system used, it can be advantageous to
use carriers composed of certain polymeric fibers. When the
capacitors or the separating layer are to be impregnated with an
organic solvent, such as a carbonate or acetonitrile for example,
the capacitor preferably comprises carriers which comprise or
consist of fibers composed of polyethylene terephthalates (PETS) or
polyamides (PAs). When the capacitors according to the present
invention are impregnated with aqueous electrolyte systems which
frequently comprise strongly alkaline or strongly acidic
electrolytes, it has been determined to be advantageous for the
carriers to comprise or consist of polymeric fibers composed of
polyacrylonitrile.
[0032] The separators which are present in the capacitor according
to the present invention as per this embodiment, which are formed
of a separating layer and a carrier, are bendable without damage
preferably down to any radius down to 100 m, preferably to a radius
in the range from 100 m down to 50 mm and most preferably to a
radius in the range from 50 mm down to 2 mm. These separators are
also notable for a breaking strength of at least 1 N/cm, preferably
at least 3 N/cm and most preferably above 6 N/cm. The high breaking
strength and the good bendability of the separator according to the
present invention has the advantage that the separator provides a
simple way of manufacturing commercially standardized wound
capacitors. In these cells, the electrode-separator plies are
spirally wound up with each other in standardized size and
contacted.
[0033] The separating layer present in this embodiment of the
capacitor has a porosity which is preferably in the range from 30%
to 70%. Porosity here refers to the accessible, i.e., open, pores.
Porosity in this sense can be determined by the familiar method of
mercury porosimetry or can be calculated from the volume and the
density of the ingredients used on the assumption that open pores
only are present. The separator present in the capacitor according
to the present invention may have a thickness in the range from 10
to 1000 .mu.m, preferably in the range from 10 to 100 .mu.m and
most preferably in the range from 10 to 50 .mu.m. The separators
are preferably less than 50 .mu.m, more preferably less than 40
.mu.m, even more preferably in the range from 5 to 30 .mu.m and
most preferably in the range from 15 to 25 .mu.m in thickness.
Separator thickness has a certain influence on the properties of
the capacitor. Thin separators permit an increased pack density in
a capacitor stack, so that a larger amount of energy can be stored
in the same volume.
[0034] In a further preferred embodiment of the capacitor according
to the present invention, the latter comprises as a carrier a
porous electrode suitable for use as an electrode in a capacitor
and forms a separator-electrode unit. More particularly, materials
useful as electrodes are materials which are useful in double-layer
capacitors or metal oxide capacitors. The separator-electrode unit
comprises a porous electrode suitable for use as an electrode in a
capacitor and a separating layer which has been applied to this
electrode and which is characterized in that it comprises particles
of the elements Al, Si and/or Zr which are adhered to each other
and to the carrier by an inorganic adhesive. The inorganic adhesive
may be for example a fraction of metal oxide particles which differ
in their average particle size, preferably by a factor of more than
10 and/or in the metal, from the particles of the elements Al, Si
and/or Zr. In a preferred embodiment of the invention, the two
particle fractions comprise metal oxide particles which differ not
only in the metal but also in their particle size. The inorganic
separating layer, as well as the inorganic constituents, may
comprise small amounts of organic and especially organosilicon
compounds. But the proportion of these organic constituents in the
inorganic separating layer is preferably less than 5% by weight,
more preferably less than 1% by weight and more preferably less
than 0.1% by weight. These silanes serve as adhesion promoters to
obtain better bonding of the ceramic to the electrodes.
[0035] The two particle fractions in the separating layer,
irrespective of whether they comprise oxides of the same or
different metals as metal oxide, preferably comprise particles
whose particle sizes differ by at least a factor of 10 and more
preferably by at least a factor of 100. Preferably, the
separator-electrode unit according to the present invention
comprises a separating layer which comprises metal oxide particles
having an average particle size (D.sub.g) greater than the average
pore size (d) of the pores of the porous electrode that are adhered
by metal oxide particles which have a particle size (D.sub.k) which
is smaller than the pores of the porous electrode. The thickness
(z) of the separating layer is preferably less than 100 D.sub.g and
not less than 1.5 D.sub.g and more preferably less than 20 D.sub.g
and not less than 5 D.sub.g.
[0036] The metal oxide particles having an average particle size
(D.sub.g) greater than the average pore size (d) of the pores of
the porous electrode are preferably Al.sub.2O.sub.3 and/or
ZrO.sub.2 particles. The metal oxide particles having an average
particle size (D.sub.k) less than the average pore size (d) of the
pores of the porous electrode are preferably SiO.sub.2 and/or
ZrO.sub.2 particles.
[0037] It is particularly preferable for the separator-electrode
units according to the present invention to comprise metal oxide
particles having an average particle size (D.sub.g) greater than
the average pore size (d) of the pores of the porous electrode an
average particle size (D.sub.g) of less than 10 .mu.m, preferably
less than 5 .mu.m and most preferably less than 3 .mu.m. A
separating layer thickness of 5 D.sub.g will thus correspond to a
separating layer thickness of about max. 15 .mu.m for particles
having an average particle size of 3 .mu.m. Preferred layer
thicknesses for the separating layer have thicknesses less than 25
.mu.m and preferably from 10 to 15 .mu.m. If necessary, however,
separating layer thickness can also be less than 10 .mu.m. The
add-on weights are preferably in the range from 10 to 200
g/m.sup.2, more preferably less than 100 g/m.sup.2 and most
preferably less than 50 g/m.sup.2.
[0038] The separating layer of the separator-electrode unit of the
capacitor according to the present invention preferably has a
porosity in the range from 30% to 70% (determined by mercury
porosimetry). Owing to the high porosity and the good wettability
of the separating layer, the separator-electrode unit and the
capacitor are readily impregnable and fillable, respectively, with
electrolytes. Furthermore, thinner separator layers permit an
increased pack density in a capacitor stack, so that a larger
amount of energy can be stored in the same volume. The
separator-electrode unit is therefore particularly useful for
capacitors having an increased energy density.
[0039] The mechanical properties of the separator-electrode unit
are essentially determined by the electrode because the separating
layer is so thin. Typical tensile strengths lie in the range of the
tensile strengths of the metallic carrier used for production. This
tensile strength is about 10 N/cm in the case of expanded metals,
depending on the expanded metal used, and more than 15 N/cm in the
case of the use of metal foils. The separator-electrode unit can be
executed to be flexible. Preferably, a separator-electrode unit
according to the present invention is bendable down to a radius
down to 100 m, preferably down to a radius in the range from 100 m
down to 50 cm and more preferably down to a radius in the range
from 50 cm down to 5, 4, 3, 2 or 1 mm.
[0040] The separator-electrode unit according to the present
invention may comprise any conventional electrode which is useful
in an electrochemical capacitor as positive or negative electrode.
Preferably, the electrode in the separator-electrode unit according
to the present invention is an electrode which is used in
double-layer capacitors or metal oxide capacitors, which thus
comprises activated carbon having a very large surface area, for
example charcoal or RuO.sub.2 or IrO.sub.2 particles. Customarily,
these compounds are combined with graphite or carbon black, a
polymer of very high thermal stability, such as polyvinylidene
fluoride, polyacrylic or polystyrene, for example, and a solvent to
create pastes which are applied to a thin metal foil (as current
collector), such as aluminum foil or copper foil for example, and
solidified by solvent removal. Preferred electrodes have a very
high porosity, preferably in the range from 20% to 40% (determined
by Hg porosimetry) to provide a very large active surface area.
What is particularly important here is not just a large specific
surface area but also that the pores have a certain minimum size in
order that they may be filled with electrolyte. Many small pores
make a large contribution to the surface area, but are ineffective
for the capacitor. The minimum size for active pores is about 5 nm.
Particularly preferred electrodes have average pore sizes (d) in
the range from 5 nm to 20 .mu.m and preferably from 10 nm to 1
.mu.m. Preference is given to multimodal pore distributions where
there are many small pores but also some large pores. The metal
foil may be coated either singly or else preferably bothsidedly.
With either electrode, the separating layer may have been applied
to either or both of the sides in the case of both sidedly coated
current collectors, depending on the further construction of the
capacitor.
[0041] A bothsided coating of at least one electrode with a
separating layer additionally simplifies the construction of a
wound module, since one of the separating layers can serve as a
separator while the other layer constitutes the insulating layer
which insulates the electrode from the counterelectrode which comes
to lie above the electrode on winding.
[0042] In a particularly preferred embodiment, the capacitor
according to the present invention comprises a separating layer
which comprises at least two fractions of oxides selected from
Al.sub.2O.sub.3, ZrO.sub.2 and/or SiO.sub.2, the first ceramic
fraction having been obtained from a sol and the second fraction
comprising particles having an average particle size in the range
from 200 nm to 5 .mu.m and the first fraction being present as a
layer on the particles of the second fraction and the first
fraction comprising from 1 to 30 parts by mass of the coating, the
second fraction being present in the ceramic coating at from 5 to
94 parts by mass of the coating and there also being present a
network comprising silicon, the silicon of the network being bonded
via oxygen atoms to the oxides of the ceramic coating, via organic
radicals to the polymeric nonwoven and via at least one chain which
comprises carbon atoms to a further silicon. The chain which
comprises carbon atoms preferably also comprises at least one
nitrogen atom. Preferably, the separating layer according to the
present invention comprises a network which comprises silicon and
in which the chains by which the silicon atoms are connected to
each other via carbon atoms, through silicon atoms connected by
chains comprising nitrogen, was obtained by addition of an amino
group onto a glycidyl group. Owing to these chains between the
silicon atoms, there is not only an inorganic network formed via
Si- or metal-oxygen bridges but also a second, organic network
which is reticulated with the first, inorganic network and which
significantly augments the stability of the membrane, especially
against water.
[0043] In a further particularly preferred embodiment of the
separating layer, the latter comprises at least three fractions of
oxides selected from Al.sub.2O.sub.3, ZrO.sub.2 and/or SiO.sub.2,
the third fraction comprising particles having an average primary
particle size in the range from 10 nm to 199 nm and the first
fraction being present as a layer on the particles of the second
and third fractions and the first fraction comprising from 1 to 30
parts by mass of the ceramic coating, the second fraction
comprising from 30 to 94 parts by mass of the ceramic coating and
the third fraction comprising from 5 to 50 parts by mass of the
ceramic coating.
[0044] In this preferred embodiment, the large particles (second
fraction) serve as a filling material for the large meshes in the
carrier. The first ceramic fraction serves as inorganic binder
(inorganic adhesive) which fixes the particles to each other and
also to the carrier (or, to be more specific, to the inorganic
silicon network formed by the adhesion promoters). The inorganic
network ensures particularly good adhesion of the ceramic coating
to organic carriers, such as polymeric nonwovens for example. The
particles of the third fraction, which have a particle size in the
middle, are believed to be responsible for the particularly good
flexibility.
[0045] It is particularly preferable for this embodiment of the
capacitor according to the present invention to comprise a
separating layer where the third fraction comprises particles
having an average primary particle size in the range from 30 nm to
60 nm and the second fraction comprises particles having an average
particle size in the range from 1 to 4 .mu.m and the first fraction
is present in the separating layer at a coating fraction in the
range from 10 to 20 parts by mass, the third fraction is present in
the separating layer at a coating fraction in the range from 10 to
30 parts by mass and the second fraction is present in the
separating layer at a coating fraction in the range from 40 to 70
parts by mass.
[0046] It can be advantageous for the third particle fraction to
contain particles which have an average aggregate or agglomerate
size in the range from 1 to 25 .mu.m. Preferably, the third
(particle) fraction contains particles which have a BET surface
area in the range from 10 to 1000 and preferably in the range from
40 to 100 m.sup.2/g.
[0047] Particularly high flexibility can be achieved for the
separating layer according to the present invention when the
particles of the third fraction are zirconium oxide or preferably
silicon oxide particles and the particles of the second fraction
are aluminum oxide particles and the ceramic fraction is formed
from silicon oxide. The medium-size particles (third fraction, such
as Sipernat, Aerosil or VP Zirkoniumoxid, all Degussa AG) and large
particles (second fraction, for example the aluminum oxides
CT800SG, AlCoA, and MZS, Martinswerke) are commercially available
particles. The first ceramic fraction comes from sols, which are
likewise commercially available or have to be produced
themselves.
[0048] Separating layers having a composition as mentioned above
are bendable (if allowed by the carrier) without damage preferably
down to any radius down to 50 m, preferably 10 cm and more
preferably 5 mm without defects arising in the separating layer as
a result.
[0049] The separators according to the present invention can
obviously also be used in all conventional capacitors.
[0050] A further embodiment of a capacitor according to the present
invention, which can be a conventional capacitor for example, may
comprise a separator-electrode unit which comprises a nonporous
polymeric film carrier onto which a metal layer is vapor deposited.
The film can be for example a polyethylene terephthalate (PET)
film. The metal used is aluminum for example. It is on this porous
metal layer as carrier, which together with the polymeric film is
preferably from 0.5 to 5 .mu.m and more preferably from 1 to 2
.mu.m in thickness, that the above-described ceramic coating is
present in a layer thickness which is preferably less than 10 .mu.m
and more preferably less than 5 .mu.m. The composition of the
ceramic separating layer can correspond to that described above.
The presence of the separating layer distinctly reduces the risk of
capacitor breakdown compared with capacitors without such a
layer.
[0051] The capacitor according to the present invention, as well as
the electrodes and the separating layer, which are customarily
accommodated in a housing and equipped with means for connecting up
the capacitor, comprises a dielectric, such as for example air in
the case of some conventional capacitors or an electrolyte, i.e., a
system of solvent and conducting salt, in the case of an
electrochemical capacitor. As well as known aqueous
solvent/conducting salt systems, the capacitor according to the
present invention may comprise in particular a nonaqueous
electrolyte selected from propylene carbonate (PC),
N,N-dimethylformamide (DMF), .gamma.-butyrolactone (GBL),
N-methyl-2-pyrrolidone (NMP) and acetonitrile (AN), and
tetraalkylphosphonium or tetraalkylammonium salts, such as for
example R.sub.4NBF.sub.4, R.sub.4NPF.sub.6, R.sub.4NClO.sub.4 or
R.sub.4NCF.sub.3SO.sub.3, where R=identical or different,
substituted or unsubstituted alkyl, aryl, alkyl-aryl, aryl-alkyl or
cycloalkyl groups, where any substituents present may be selected
from primary, secondary or tertiary alkyl groups, alicyclic groups,
aromatic groups, --N-dialkyl, --NHalkyl, --NH.sub.2, fluorine,
chlorine, bromine, iodine, --CN, --OH--C(O)-alkyl, --C(O)H or
C(O)O-alkyl, --CF.sub.3, --O-alkyl, --C(O)N-alkyl and/or
--OC(O)-alkyl, as conducting salts. As described above, the
separating layer or the carrier must be chosen according to the
electrolyte to be used.
[0052] The capacitor according to the present invention can be
produced in the same way as all prior art capacitors. The
separating layer which is present in the capacitor according to the
present invention on and/or in a porous carrier or on the carrier
is obtainable for example by applying a suspension to the carrier
and solidifying the suspension by at least single heating on and/or
in the carrier, the suspension comprising a sol as inorganic
adhesive and at least one fraction of oxidic particles selected
from the oxides of the elements Al, Zr and/or Si.
[0053] Depending on whether the separating layer is to be applied
to an electrode or to a carrier which is not suitable for use as an
electrode, an appropriate carrier has to be used. A carrier which
is not suitable for use as an electrode is preferably less than 30
.mu.m, more preferably less than 20 .mu.m and even more preferably
from 10 to 20 .mu.m in thickness. It is particularly preferable to
use carriers as described in the preceding description of the
capacitor according to the present invention. The porous carrier
used thus preferably comprises woven or non-woven polymeric or
glass fibers. It is particularly preferable for the carrier used to
comprise a glass or polymeric woven or nonwoven or to be such a
woven or nonwoven. Preferably, the carrier used comprises polymeric
fibers having a softening temperature of above 100.degree. C. and a
melting temperature of above 110.degree. C. It can be advantageous
for the polymeric fibers to be from 0.1 to 10 .mu.m and preferably
from 1 to 5 .mu.m in diameter. It is particularly preferable for
the process according to the present invention to utilize a carrier
which comprises fibers selected from polyacrylonitrile, polyester,
polyamide and/or polyolefin.
[0054] When the carrier used is an electrode, any conventional
electrode which is suitable for use as an electrode in a capacitor
can be used. Such electrodes for electrochemical capacitors
customarily comprise a metal foil current collector having, on
either or both sides of the foil, an applied porous coating of an
electroconductive material, such as RuO.sub.2 or IrO.sub.2
particles or activated carbon particles for example, which are
conductively connected to each other and to the current collector
by carbon black and graphite and a binder. For conventional
capacitors, the electrodes comprise a metal layer on a polymeric
film.
[0055] The production of ceramic coatings of the kind constituting
the separating layers in capacitors according to the present
invention is known in principle from WO 99/15262.
[0056] The separating layers according to the present invention are
obtained by applying a suspension which inorganic
nonelectroconductive particles to a preferably porous
electroconductive carrier (an electrode for example) or a
nonelectroconductive carrier (polymeric nonwoven) and then
solidifying the suspension to form an inorganic coating on and/or
in the porous carrier. The suspension may be applied to the carrier
by printing on, pressing on, pressing in, rolling on, knifecoating
on, spreadcoating on, dipping, spraying or pouring on for
example.
[0057] The suspension used for producing the coating comprises at
least particles of Al.sub.2O.sub.3, ZrO.sub.2 and/or SiO.sub.2 and
at least one sol of the elements Al, Zr and/or Si and is produced
by suspending the particles in at least one of these sols. The
suspending is effected by intensive mixing of the components. The
average size of the particles used is preferably in the range from
0.5 to 10 .mu.m and more preferably in the range from 1 to 5 .mu.m.
The metal oxide particles used for producing the suspension are
more preferably aluminum oxide particles, which preferably have an
average particle size in the range from 0.5 to 10 .mu.m, and more
preferably from 1 to 5 .mu.m. Aluminum oxide particles in the range
of the preferred particle sizes are available for example from
Martinswerke under the designations MZS 3 and MZS 1 and from AlCoA
under the designation CT3000 SG, CL3000 SG, CT1200 SG, CT800SG and
HVA SG.
[0058] It has been determined that the use of commercially
available oxidic particles leads to unsatisfactory results in
certain circumstances, since the particle size distributions are
frequently very wide. It is therefore preferable to use metal oxide
particles which have been classified by a conventional process, for
example wind sifting and hydroclassification. It is preferable to
employ as oxidic particles those fractions where the coarse grain
fraction, which accounts for up to 10% of the total amount, has
been separated off by wet sieving. This unwelcome coarse grain
fraction, which is very difficult or impossible to comminute even
by the typical processes of suspension production such as, for
example, grinding (ball mill, attritor mill, pestle mill),
dispersing (Ultra-Turrax, ultrasound), trituration or chopping, can
consist for example of aggregates, hard agglomerates, grinding
media attritus. The aforementioned measures ensure that the
inorganic porous layer has a very uniform pore size distribution.
This is achieved in particular by using oxidic particles whose
maximum particle size is preferably from 1/3 to 1/5 and more
preferably not more than 1/10 of the thickness of the carrier
(nonwoven) used.
[0059] Table 2 hereinbelow gives an overview of how the choice of
the various aluminum oxides affects the porosity and the resulting
pore size of the respective porous inorganic separating layer. To
determine these data, the corresponding slips (suspensions or
dispersions) were prepared and dried and solidified as pure
moldings at 200.degree. C. TABLE-US-00001 TABLE 2 Typical data of
ceramics as a function of powder type used Average pore
Al.sub.2O.sub.3 type Porosity/% size/nm AlCoA CL3000SG 51 755 AlCoA
CT800SG 53.1 820 AlCoA HVA SG 53.3 865 AlCoA CL4400FG 44.8 1015
Martinsw. DN 206 42.9 1025 Martinsw. MDS 6 40.8 605 Martinsw. MZS 1
+ 47% 445 Martinsw. MZS 3 = 1:1 Martinsw. MZS 3 48% 690
[0060] By average pore size and the porosity are meant the average
pore size and the porosity as may be determined by the known method
of mercury porosimetry using for example a 4000 porosimeter from
Carlo Erba Instruments. Mercury porosimetry is based on the
Washburn equation (E. W. Washburn, "Note on a Method of Determining
the Distribution of Pore Sizes in a Porous Material", Proc. Natl.
Acad. Sci., 7, 115-16 (1921)).
[0061] The mass fraction of the suspended component (particles) is
preferably from 1 to 250 times and more preferably from 1 to 50
times the sol used.
[0062] The sols are obtained by hydrolyzing at least one
(precursor) compound of the elements Zr, Al and/or Si. It can
likewise be advantageous for the compound to be hydrolyzed to be
introduced into alcohol or an acid or a combination thereof prior
to hydrolysis. The compound to be hydrolyzed is preferably at least
one nitrate, one chloride, one carbonate or one alkoxide compound
of the elements Zr, Al and/or Si. The hydrolysis is preferably
carried out in the presence of liquid water, water vapor, ice,
alcohol or an acid or a combination thereof. Preferably, the sols
are obtained by hydrolyzing a compound of the elements Al, Zr or Si
using water or a an acid or a combination thereof, the compounds
preferably being present dissolved in an anhydrous solvent and
being hydrolyzed with from 0.1 to 100 times the molar ratio of
water.
[0063] In one version of the process for producing the separating
layer of the present invention, particulate sols are produced by
hydrolysis of the compounds to be hydrolyzed. These particulate
sols are so called because the compounds formed by hydrolysis in
the sol are present in particulate form. Particulate sols can be
prepared as described above or in WO 99/15262. These sols
customarily have a very high water content, which is preferably
above 50% by weight. It can be advantageous for the compound to be
hydrolyzed to be introduced into alcohol or an acid or a
combination thereof prior to hydrolysis. The hydrolyzed compound
may be peptized by treatment with at least one organic or inorganic
acid, preferably with a 10-60% organic or inorganic acid, more
preferably with a mineral acid selected from sulfuric acid,
hydrochloric acid, perchloric acid, phosphoric acid and nitric acid
or a mixture thereof. The particulate sols thus produced can
subsequently be used to produce suspensions, in which case it is
preferable to produce suspensions for application to polymeric
fiber nonwovens which have been pretreated with polymeric sol.
[0064] In a further version of the process for producing a
separating layer according to the present invention, polymeric sols
are produced by hydrolysis of the compounds to be hydrolyzed. These
polymeric sols are so called because the compounds formed by
hydrolysis in the sol are present in polymeric form, i.e., in the
form of chains crosslinked across a relatively large space.
Polymeric sols customarily contain less than 50% by weight,
preferably very much less than 20% by weight, of water and/or
aqueous acid. To obtain the preferred fraction of water and/or
aqueous acid, the hydrolysis is preferably carried out in such a
way that the compound to be hydrolyzed is hydrolyzed with from 0.5
to 10 times the molar ratio and preferably with half the molar
ratio of liquid water, water vapor or ice, based on the
hydrolyzable group, of hydrolyzable compound. The amount of water
used can be up to 10 times in the case of compounds which are very
slow to hydrolyze, such as tetraethoxysilane for example. Compounds
which are very quick to hydrolyze, such as zirconium tetraethoxide,
may well form particulate sols under these conditions, for which
reason 0.5 times the amount of liquid water is preferably used to
hydrolyze such compounds. A hydrolysis with less than the preferred
amount of liquid water, water vapor or ice likewise leads to good
results, although using more than 50% less than the preferred
amount of half the molar ratio is possible but not very sensible,
since hydrolysis would no longer be complete and coatings based on
such sols would not be very stable.
[0065] To produce these sols having the desired very low fraction
of water and/or acid in the sol, it may be preferable for the
compound to be hydrolyzed to be dissolved in an organic solvent,
especially ethanol, isopropanol, butanol, amyl alcohol, hexane,
cyclohexane, ethyl acetate or mixtures thereof, before the actual
hydrolysis is carried out. A sol thus produced can be used for
producing the suspension of the present invention or as an adhesion
promoter in a pretreatment step. It is particularly preferable to
use a suspension for producing the inventive separating layer which
comprises a polymeric sol of a compound of silicon.
[0066] Both particulate sols and polymeric sols are useful as a sol
in the inventive process for preparing the suspension. As well as
sols obtainable as just described, it is in principle also possible
to use commercially available sols, for example zirconium nitrate
sol or silica sol. The process for producing separating layers or
separators by applying a suspension to, and solidifying it on, a
carrier is known per se from DE 101 42 622 and in similar form from
WO 99/15262, but not all the parameters and ingredients are
applicable to the production of the separator used in the process
according to the present invention. More particularly, the
operation described in WO 99/15262 is in that form not fully
applicable to polymeric nonwoven materials, since the very watery
sol systems described therein frequently do not permit complete,
in-depth wetting of the customarily hydrophobic polymeric
nonwovens, since most polymeric nonwovens are only badly wetted by
very watery sol systems, if at all. It has been determined that
even the minutest unwetted areas in the nonwoven material can lead
to membranes and separators being obtained that have defects (such
as holes or cracks, for example) and hence are inutile.
[0067] It has been found that a sol system or suspension whose
wetting behavior has been adapted to the polymers will completely
penetrate the carrier materials and especially the nonwoven
materials and so provide defect-free coatings. In the inventive
process it is therefore preferable to adapt the wetting behavior of
the sol or suspension. This is preferably accomplished by producing
polymeric sols or suspensions from polymeric sols, these sols
comprising one or more alcohols, for example, methanol, ethanol or
propanol or mixtures thereof which also preferably comprise
aliphatic hydrocarbons. But other solvent mixtures are conceivable
as well for addition to the sol or suspension in order that the
wetting behavior thereof may be adapted to the nonwoven (carrier)
used.
[0068] To improve the adhesion of the inorganic components to
polymeric fibers or nonwovens as carrier, it may be preferable for
the suspensions used to be admixed with adhesion promoters, for
example organofunctional silanes, for example the Degussa silanes
GLYMO, MEMO, AMEO, VTEO or Silfin. The admixing of adhesion
promoters is preferable in the case of suspensions based on
polymeric sols. Useful adhesion promoters include especially
compounds selected from the octylsilanes, the vinylsilanes, the
amine-functionalized silanes and/or the glycidyl-functionalized
silanes, for example the Dynasilanes from Degussa. Particularly
preferred adhesion promoters are vinyl-, methyl- and octylsilanes
for polyethylene (PE) and polypropylene (PP) (although the
exclusive use of methylsilanes is not optimal), amine-functional
silanes for polyamides and polyamines and glycidyl-functionalized
silanes for polyacrylates, polyacrylonitrile and polyesters.
Triethoxy(tridecafluoroochyl)silane, for inslaxe, is highly
suitable for PVDF. Other adhesion promoters can be used as well,
but they have to be adapted to the respective polymers. Adhesion
promoters have to be chosen such that the solidification
temperature is below the melting or softening temperature of the
polymer used as a substrate and below the decomposition temperature
of the polymer. The adhesion promoters used are especially the
silanes listed in table 1. Preferably, suspensions according to the
present invention contain very much less than 25% by weight and
preferably less than 10% by weight of compounds capable of acting
as adhesion promoters. An optimal fraction of adhesion promoter
results from coating the fibers and/or particles with a
monomolecular layer of adhesion promoter. The amount in grams of
adhesion promoter required for this purpose can be obtained by
multiplying the amount (in g) of the oxides or fibers used by the
specific surface area of the materials (in m.sup.2g.sup.-1) and
then dividing by the specific area required by the adhesion
promoters (in m.sup.2g.sup.-1), the specific area required
frequently being in the range from 300 to 400 m.sup.2g.sup.-1 in
order of magnitude.
[0069] Table 2 below contains an illustrative selection of
preferred adhesion promoters based on organofunctional silicon
compounds for typical polymers used as a nonwoven material.
TABLE-US-00002 TABLE 2 Polymer Organofunctional type Adhesion
promoter PAN Glycidyl GLYMO methacryloyl MEMO PA Amino AMEO, DAMO
PET methacryloyl MEMO vinyl VTMO, VTEO, VTMOEO PE, PP amino AMEO,
AMMO vinyl VTMO, VTEO, Silfin methacryloyl MEMO where: AMEO =
3-aminopropyltriethoxysilane DAMO =
2-aminoethyl-3-aminopropyltrimethoxysilane GLYMO =
3-glycidyloxytrimethoxysilane MEMO =
3-methacryloyloxypropyltrimethoxysilane Silfin = vinylsilane +
initiator + catalyst VTEO = vinyltriethoxysilane VTMO =
vinyltrimethoxysilane VTMOEO = vinyltris(2-methoxyethoxy)silane
[0070] The suspension present on and/or in the carrier as a result
of having been applied thereto (the coating) can be solidified by
heating to a temperature in the range from 50 to 350.degree. C. for
example. Since, when polymeric substrate materials are used, the
maximum allowable temperature is dictated by the carrier material,
the maximum allowable temperature has to be adapted accordingly so
that the carrier material does not melt or soften. Thus, depending
on the embodiment of the process, the suspension present on and in
the carrier is solidified by heating at from 100 to 350.degree. C.
and most preferably by heating at from 200 to 280.degree. C. It may
be preferable for the heating to take place at from 150 to
350.degree. C. for from 1 second to 60 minutes. It is particularly
preferable to solidify the suspension by heating at from 110 to
300.degree. C. and most preferably at from 170 to 280.degree. C.
and preferably for from 0.5 to 10 min. Heating the suspension
preferably takes from 0.5 to 10 minutes at from 200 to 220.degree.
C. on a polymeric nonwoven comprising fibers composed of polyester,
and from 0.5 to 10 minutes at from 170 to 200.degree. C. on a
polymeric nonwoven comprising fibers composed of polyamide. The
heating of the assembly may be effected by means of heated air, hot
air, infrared radiation or by other heating methods according to
the prior art.
[0071] The process for producing separating layers according to the
present invention can be carried out for example by unrolling the
carrier off a reel, passing it at a speed in the range from 1 m/h
to 2 m/s, preferably at a speed in the range from 0.5 m/min to 20
m/min and most preferably at a speed in the range from 1 m/min to 5
m/min through at least one apparatus which applies the suspension
onto and into the carrier, such as a roll for example, and at least
one further apparatus which enables the suspension to be solidified
on and in the carrier by heating, for example an electrically
heated oven, and rolling the carrier which has been provided with a
separating layer up on a second reel. This makes it possible to
produce the separating layer in a continuous process. Similarly,
the pretreatment steps can be carried out as a continuous process
while retaining the parameters mentioned.
[0072] In a further preferred embodiment of the inventive process
for producing the separating layer by at least single heating of a
suspension on and in the carrier, especially polymeric nonwoven, is
solidified, the suspension comprising a sol and at least one
fraction of oxidic particles selected from the oxides of the
elements Al, Zr, Ti and/or Si, is notable in that the suspension
has added to it prior to application a mixture of at least two
different adhesion promoters which are each based on an
alkylalkoxysilane of the general formula I R.sub.x--Si(OR).sub.4-x
(I) where x=1 or 2 and R=organic radical, the radicals R being the
same or different, the adhesion promoters being selected so that
both the adhesion promoters comprise alkyl radicals which at least
each comprises a reactive group as a substituent, the reactive
group on the alkyl radical of one adhesion promoter reacting with
the reactive group of the other adhesion promoter during the at
least single heating to form a covalent bond, or one or more
adhesion promoters as per the formula I, which have reactive groups
which are capable of reacting under the action of UV radiation to
form a covalent bond, the addition of an adhesion promoter which
reacts under the action of UV radiation being followed by one or
more treatments with UV radiation after the suspension has been
applied to the polymeric nonwoven (carrier). The treatment with UV
radiation can be effected for example by means of a UV lamp, in
which case the amount of energy received has to be sufficient to
ensure crosslinking of the adhesion promoters. Good results are
obtained for example by treatment with a mercury vapor lamp for a
period in the range from 0.1 to 24 hours and preferably in the
range from 1 to 4 hours. The treatment with UV radiation may be
carried out before or after the at least single heating.
Preferably, the UV treatment is carried out after the suspension
has been applied to the polymeric nonwoven (carrier) and before the
single heating of the suspension.
[0073] The use of at least two of the adhesion promoters mentioned
is believed to lead to the formation, during the production of the
separating layer, of a network which comprises silicon, the silicon
of the network being bonded via oxygen atoms to the oxides of the
ceramic coating, via organic radicals to the polymeric nonwoven
(carrier) and via at least one chain comprising carbon atoms to a
further silicon. It is believed that the same effect is achieved
through an at least single treatment with UV radiation when a
UV-active adhesion promoter is added to the suspension. Owing to
the chains between the silicon atoms, there is not only an
inorganic network, formed via Si- or metal-oxygen bridges, but also
a second, organic network which is reticulated with the first,
inorganic network and which significantly augments the stability of
the separating layer, especially against water.
[0074] Useful adhesion promoters include in principle all adhesion
promoters which satisfy the abovementioned formula I and where at
least two adhesion promoters each have an alkyl radical which is
capable of entering into a chemical reaction with the alkyl radical
of the other adhesion promoter to form a covalent bond. In
principle, all chemical reactions are feasible, but an addition or
condensation reaction is preferable. The adhesion promoters may
each have two or one alkyl radical (x in formula I being 1 or 2).
Preferably, the adhesion promoters used in the process according to
the present invention which have a reactive group on the alkyl
radical have only one alkyl radical (x=1). The at least two
adhesion promoters employed in the process of the present invention
can be for example an adhesion promoter having an amino group on
the alkyl radical and an adhesion promoter having a glycidyl group
on the alkyl radical. It is particularly preferable for the process
of the present invention to employ 3-aminopropyltriethoxysilane
(AMEO) and 3-glycidyloxytrimethoxysilane (GLYMO) as adhesion
promoters. Preferably, the molar ratio of the two adhesion
promoters to each other is in the range from 100:1 to 1:100 and
preferably in the range from 2:1 to 1:2 and most preferably about
1:1. Methacryloyloxypropyltrimethoxysilane (MEMO) is preferably
used as a UV-active adhesion promoter which is capable of forming a
covalent bond between the adhesion promoter molecules under the
action of UV radiation. The adhesion promoters are available from
Degussa AG for example.
[0075] To obtain a sufficiently stable network, the suspension of
the present invention preferably comprises an adhesion promoter
fraction in the range from 0.1 to 20 mass % and preferably in the
range from 2 to 10 mass %. As well as the "reactive" adhesion
promoters mentioned, the suspension may comprise further adhesion
promoters selected from the organofunctional silanes mentioned
above. These adhesion promoters can likewise be present in the
suspension at a fraction in the range from 0.1 to 20 mass % and
preferably at a fraction in the range from 2 to 10 mass %.
[0076] A further preferred embodiment of the process according to
the present invention utilizes a suspension which comprises a sol
and at least two fractions of oxidic particles selected from the
oxides of the elements Al, Zr, Ti and/or Si and at least one first
fraction comprises primary particles having an average particle
size in the range from 200 nm to 5 .mu.m and from 30 to 94 parts by
mass of the suspension and at least one second fraction comprises
an average primary particle size in the range from 10 nm to 199 nm
and from 5 to 50 parts by mass of the suspension. Additionally, the
suspension may in turn comprise adhesion promoters, including
especially the abovementioned reactive adhesion promoters. The
particles of the first fraction are preferably aluminum oxide
particles and are offered for example by Martinswerke under the
designations MZS 3 and MZS1 and by AlCoA under the designation
CT3000 SG, CL3000 SG, CT1200 SG, CT800SG and HVA SG. Aluminum
oxide, silicon oxide and zirconium oxide particles of the second
fraction are offered for example by Degussa AG under the
designations Sipernat, Aerosil, Aerosil P25 or Zirkoniumoxid
VP.
[0077] It is particularly preferable to use suspensions where the
mass fraction of the suspended component (second and third particle
fractions) is from 1.5 to 250 times and more preferably from 5 to
20 times the employed first fraction from the sol.
[0078] When an electrode is coated as a carrier using the process
according to the present invention, it will be advantageous for the
separating layer not to be present in the electrode which is used
as a carrier. To ensure this, it will be advantageous for the
suspension used to preferably comprise metal oxide particles having
an average particle size (D.sub.g) greater than the average pore
size (d) of the pores of the porous electrode. The metal oxide
particles or the metal oxide particles having an average particle
size (D.sub.g) greater than the average pore size (d) of the pores
of the porous electrode that are used for preparing the suspension
are preferably Al.sub.2O.sub.3 and/or ZrO.sub.2 particles. It is
particularly preferable for the particles used as metal oxide
particles to have an average particle size of less than 10 .mu.m,
preferably less than 5 .mu.m and most preferably less than 3
.mu.m.
[0079] To use a suspension having particles which are smaller than
the average pore size of the pores of the electrode, it may be
necessary to adjust the viscosity of the suspension. An
appropriately high suspension viscosity will absent external
shearing forces prevent penetration of the suspension into the
pores of the electrode used as a carrier (structural viscosity,
nonnewtonian behavior). Such a behavior can be achieved through
addition of auxiliaries that influence the flow behavior.
Suspension viscosity is likewise preferably adjusted using
inorganic materials as auxiliaries. It is particularly preferable
to add pyrogenic silicas, for example Aerosils from Degussa AG, for
example Aerosil 200, to the suspension to adjust suspension
viscosity. Since these substances are very effective when used as
auxiliaries to adjust the viscosity, it is sufficient for the
silica mass fraction of the suspension to be in the range from 0.1%
to 10% by weight and preferably from 0.5% to 5% by weight.
[0080] The thus produced carrier with separating layer may be used
(depending on the carrier material used) as a separator or as a
separator-electrode unit together with other components which are
necessary for a capacitor as per the prior art to assemble a
capacitor. When the capacitor thus produced is an electrochemical
capacitor, the separating layer between the electrodes additionally
has to be filled with the electrolyte system before the capacitor
housing can be sealed.
[0081] The thus produced capacitors according to the present
invention can be used as stores for electric energy in vehicles,
electrovehicles, in starter modules for engines, especially diesel
assemblies, disruptionless power supplies and in any technical
appliance in which very large electric power outputs are required
for short periods only.
[0082] The examples which follow describe the present invention
without the scope of the claims and the description being
restricted by the examples.
EXAMPLES
Example 1
Inventive Separator S450P
[0083] To 130 g of water and 15 g of ethanol were initially added
30 g of a 5% by weight aqueous HNO.sub.3 solution, 10 g of
tetraethoxysilane, 2.5 g of methyltriethoxysilane and 7.5 g of
GLYMO Dynasilane. This sol, which was initially stirred for some
hours, was only used to suspend 125 g each of the aluminum oxides
Martoxid MZS-1 and Martoxid MZS-3. This slip was homogenized with a
magnetic stirrer for at least a further 24 h, during which the
stirred vessel had to be covered over in order that no solvent loss
occurred.
[0084] The above slip was then used to coat a 20 cm wide PET
nonwoven having a thickness of about 20 .mu.m and a basis weight of
about 15 g/m2 in a continuous roll coating process at a belt speed
of about 30 m/h and T=200.degree. C. where the slip is rolled onto
the nonwoven by a roll which turns in the direction opposite to the
belt direction (and direction of movement of the nonwoven). The
nonwoven subsequently passes through an oven 1 m in length which
has the stated temperature. The same method and arrangement for
coating is used in the runs which follow. The end result obtained
is a separator having an average pore size of about 450 nm and 35
.mu.m thickness.
Example 2
Inventive Capacitor
[0085] A copper foil 165 mm in width is coated over 160 mm width
with a dispersion of 10 g of highly activated carbon (1200
m.sup.2/g, obtained as per BET method, as described in
Winnacker-Kuchler (3.) 7, 93f. Z. Anal. Chem. 238, 187-193 (1968))
and 1 g of PVDF in 89 g of NMP continuously by means of the roll
coating process known from Example 1 (belt speed about 30 m/h,
T=150.degree. C.). This material is used as an electrode
hereinafter.
[0086] The separator as per Example 1 is initially trimmed to a
width of about 165 mm and then processed together with two
electrodes to form a coil having about 150 windings (electrode
pairs with respectively 2 separator plies). The coil is inserted
into an aluminum housing 50 mm in diameter and 172 mm in height,
electrically connected to the external terminals and filled up with
the electrolyte (concentrated solution of tetraethylammonium
borofluoride in acetonitrile).
[0087] The capacitor will have a weight of about 400 g, a capacity
of about 1850 farads at a voltage of 2.5 V. The maximum current is
450 A.
Example 3
Inventive Separator-Electrode Unit
[0088] A copper foil 165 mm in width is coated over 160 mm width
with a dispersion of 10 g of highly activated carbon (1200
m.sup.2/g, determined as per BET method and 1 g of PVDF in 89 g of
NMP continuously by means of the roll coating process known from
Example 1 (belt speed about 30 m/h, T=150.degree. C.). The coating
is effected concurrently on both sides.
[0089] To 130 g of water and 15 g of ethanol were initially added
30 g of a 5% by weight aqueous HNO.sub.3 solution, 10 g of GLYMO
Dynasilane and 10 g of GLYMO Dynasilane. This sol, which was
initially stirred for some hours, was then used to suspend 200 g of
CT1200SG aluminum oxide. This slip was homogenized with a magnetic
stirrer for at least a further 24 h, during which the stirred
vessel had to be covered over in order that no solvent loss
occurred.
[0090] This electrode is coated with this slip in a second step on
one side only over a width of 162 mm using the known roll coating
process (belt speed about 60 m/h, T=180.degree. C.).
Example 4
Inventive Capacitor
[0091] Two separator-electrode units consisting of an electrode as
per Example 3, endowed with a separator layer on one side, are
processed into a coil, care being taken to ensure that the
electrodes are cleanly separated from each other at all times by a
ceramic separator layer. This coil is inserted into an aluminum
housing 60 mm in diameter and 172 mm in height, electrically
connected to the outer terminals and filled up with the electrolyte
(concentrated solution of tetraethylammonium borofluoride in
acetonitrile).
[0092] The capacitor will have a weight of about 525 g, a capacity
of about 2700 farads at a voltage of 2.5 V. The maximum current is
600 A.
* * * * *